`pandas` v3 Chained Assignment future proofing

[hsteptoe]

📰 Custom Issue

A note that iris.pandas will need to be updated to account for breaking changes expected in pandas v3 in the way it handles chained assignments.

Helpfully, tests currently run with the following warnings and suggested changes:

FutureWarning: ChainedAssignmentError: behaviour will change in pandas 3.0!
  You are setting values through chained assignment. Currently this works in certain cases, but when using Copy-on-Write (which will become the default behaviour in pandas 3.0) this will never work to update the original DataFrame or Series, because the intermediate object on which we are setting values will behave as a copy.
  A typical example is when you are setting values in a column of a DataFrame, like:
  
  df["col"][row_indexer] = value
  
  Use `df.loc[row_indexer, "col"] = values` instead, to perform the assignment in a single step and ensure this keeps updating the original `df`.